System and method for verifying delivery and integrity of electronic messages

ABSTRACT

The invention provides a system and method for determining when a message is received by a recipient or an agent for the recipient. A link is activated at the recipient to provide an indication that the message has been opened by the recipient. The activation of the link may cause a server remote from the recipient to take some further action.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/448,305, filed Apr. 16, 2012, now U.S. Pat. No. 8,468,198, issuedJun. 18, 2013, which is a continuation of U.S. application Ser. No.12/838,340, filed Jul. 16, 2010, now U.S. Pat. No. 8,161,104, issuedApr. 17, 2012, which is a continuation of U.S. application Ser. No.09/626,577, filed Jul. 27, 2000, now U.S. Pat. No. 7,966,372, issuedJun. 21, 2011, which claims benefit to U.S. Provisional Application No.60/172,479, filed Dec. 17, 1999 and U.S. Provisional Application No.60/146,074 filed Jul. 28, 1999, the contents of which are herebyincorporated by reference in their entirety. Applicants claim priorityto all of the applications in the chain.

The subject matter of this application is related to U.S. applicationSer. No. 10/722,238, filed Nov. 24, 2003, now Abandoned.

BACKGROUND

Field of Invention

This invention relates generally to a system and method for verifyingdelivery and content of an electronic message and, more particularly, toa system and method of later providing proof regarding the delivery andcontent of an e-mail message.

Description of the Related Art

In recent years e-mail has become an indispensable business tool. E-mailhas replaced “snail mail” for many business practices because it isfaster, cheaper and generally more reliable. But there remain some mailapplications where hard copy is still dominant, such as registered andcertified mail. For example, when a letter is sent by certified mail thesender is provided with a receipt to prove that the letter was mailed. Areturned registered mail receipt adds the Postal Service's confirmationthat the letter was successfully delivered to the addressee or theaddressee's authorized agent. Additionally, private couriers such asFederal Express® and United Parcel Service® (UPS) provide some type ofdelivery confirmation. Since every piece of courier mail is, in effect,registered it is natural for consumers to turn to these services whenthey want proof of delivery.

Many existing e-mail systems and e-mail programs already provide forsome form of proof of delivery. For instance, some e-mail systems todayallow a sender to mark a message with “request for notifications” tags.Such tags allow a sender to request notification that the message wasdelivered and/or when the message was opened. When a sender requestsdelivery notification, the Internet e-mail system may provide the senderwith an e mail receipt that the message was delivered to the mail serveror electronic inbox of the recipient. The receipt message may includethe title of the message, the destination address, and the time ofdelivery. It may also include (depending on the types of “flags” thatare provided and activated in the mailing software) a list of all theInternet “stations” that the message passed through en route to itsdestination. This form of reporting is built into some of the rules andprotocols which implement e-mail. Furthermore, when a message is sentwith a “read notification” request, the recipient's email program maysend to the sender an e-mail notification that the recipient opened thatmessage for reading. Many electronic mail clients can and do supportthis kind of reporting; however. Internet protocols do not make thismandatory.

However, this does not mean that an e-mail sent with a notificationrequest is as effective in all respects as registered mail. Peoplecertify and register letters because they want proof of delivery, e.g.,proof that can be used in a civil or criminal proceeding, or proof thatwill satisfy a supervisor or a client or a government agency that amessage has been sent, a job has been done, an order placed, or acontract requirement satisfied.

A registration receipt from the United States Postal Service (USPS)constitutes proof of delivery because the USPS stands behind it. Thereceipt represents the Post Office's confirmation that the letter orpackage in question was actually delivered to the addressee or hisauthorized representative. On the other hand, with the e-mail receiptvarious hurdles exist to an e-mail receipt being admitted and reliedupon as persuasive evidence in a court of law as a proof that themessage was delivered. After all, the receipt may be just another e-mailmessage that could have been altered or created by anyone, at any time.

There exists a need for an e-mail system and/or method that can providereliable proof of the content and delivery of an e-mail message in orderto take fuller advantage of the convenience and low cost ofcommunicating via e-mail.

To meet this need some systems have been established whereby senders mayreceive third party proof of delivery by enrolling in services whereby:

a) The sender transmits an electronic message to a third party togetherwith a list of the document's intended recipients.

b) The third party sends a notification to each of the message'sintended recipients inviting them to visit the third party's web sitewhere the message can be viewed.

c) If the intended recipient visits the third party's web site to viewthe message, the third party records this visit so that the sender mayknow that his message has been read by the recipient.

The drawbacks of such systems are manifold. In the first place they relyessentially on the co-operation of the recipient of the e-mail tocollect their messages from the third party's service. But thecircumstances in which a sender may want proof of delivery of a messageare often ones in which it cannot be assumed that the intended recipientwill co-operate in receiving the message. In such cases, e.g. whereacknowledging receipt of the message would place a financial or legalburden on the recipient, the recipient can simply ignore thenotification that mail is available for him to receive. Note that thereis nothing in such a system to guarantee that the intended recipient hasreceived notification of waiting mail. In the second place, such systemsare cumbersome and slow to use as compared to regular e-mail insofar asit can require the sender and/or the recipient to connect to a WorldWide Web site to send, collect and verify the delivery of each message.Moreover, transmission of documents by such methods may require bothsender and receiver to upload and download files to a web site. Finally,because these methods require the third party to retain a copy of thewhole of each message until such time as they are collected or expired,the methods can require its provider to devote substantial computationalresources to data storage and data tracking over an extended period oftime. As an alternative method of providing proof of delivery, somesystems provide proprietary e-mail clients or web-browser plug-ins thatwill notify senders when a message has been received provided that arecipient uses the same e-mail client. The obvious disadvantage of suchsystems is that they require both sender and recipient to use the samee-mail client.

Therefore, there exists a need for an e-mail system/method that canprovide reliable proof of the content and delivery of electronicmessages which does not require the compliance or co-operation of therecipient, which requires no special e-mail software on the part ofsender or recipient. which operates with the same or nearly the sameconvenience and speed of use as conventional e-mail, and which can beoperated economically by a service provider.

SUMMARY OF THE INVENTION

A general objective of the present invention is to provide a system andmethod for reliably verifying via secure and tamper-proof documentationthe content and delivery of an electronic message such as an e-mail.Ideally, the invention will give e-mail and other electronic messages alegal status on a par with, if not superior to, that of registeredUnited States mail. However, it is not necessary to the invention thatany particular legal status is accorded to messages sent according tothe methods taught herein, as the invention provides useful informationand verification regardless.

The present invention includes an electronic message system that createsand records a digital signature of each electronic message sent throughthe system. An originator may send a copy of the electronic message tothe system or generate the electronic message within the system itself.The system then forwards and delivers the electronic message to allrecipients (or to the designated message handlers associated with therecipients), including “to” addressees and “cc” addressees. Thereafter,the system returns a receipt of delivery to the originator of theelectronic message. The receipt includes, among other things: theoriginal message. the digital signature of the message, and ahandshaking and delivery history including times of delivery to therecipients. To later verify and authenticate information contained inthe receipt, the originator or user sends a copy of the receipt to thesystem. The system then verifies that the digital signature matches theoriginal message and the rest of the receipt. If the two match, then thesystem sends a letter or provides other confirmation of authenticityverifying that the electronic message has not been altered.

The system may be a form of e-mail server connected to the Internet,which can be utilized in many ways. For instance, individual users canregister their electronic messages, such as e-mails, by sending a“carbon copy” (cc:) to the system or composing the message within thesystem itself. For corporate or e-commerce users, these users can changetheir server to a server incorporating the present invention and haveall of their external electronic messages registered, with the option ofhaving the system retain and archive the receipts. The system can acceptand verify encrypted electronic messages and manage the electronicmessages within and/or outside a “fire wall.” For web-based users, i.e.,individuals or corporations using web-based e-mails, such as MSNHotmail®, or Yahoo Mail®, such users could check a box or otherwise seta flag within their e-mail programs to select on a case-by-case basiswhether to register the e-mails and/or to archive the messages using thepresent system.

The digital signature can be created using known digital signaturetechniques. such as by performing a hash function on the message toproduce a message digest and then encrypting the message digest.Separate digital signatures can be created for the body of the message,any attachments, and for the overall message including the body, theattachments, and the individual message digests. The encrypted messagedigest provides one type of message authentication or validation code,or secure documentation. Other message authentication and/or validationcodes may also be generated and used.

In one aspect, the invention is a method of providing proof regardingthe delivery and content of an electronic message, comprising: receivingfrom a sender across a computer network an electronic message, themessage having a delivery address associated therewith; computing amessage digest according to the message; encrypting the message digest;sending the message electronically to a destination corresponding to thedelivery address; recording the Simple Mail Transport Protocol (SMTP) orExtended SMTP (ESMTP) dialog which effects the delivery of the message;receiving Delivery Status Notification information associated with themessage and the delivery address; providing to the sender an electronicreceipt, the receipt comprising: a copy of the message, the encryptedmessage digest, the (E)SMTP transcripts, and at least a subset of theDelivery Status notification information, and, at a future date,receiving electronically the electronic receipt from the sender,verifying that the encrypted message digest corresponds to the message,and verifying that the message was received by an electronic messagehandler associated with the delivery address.

In another aspect, the invention is a method of verifying delivery of anelectronic message, comprising: in a wide area network computer system,receiving an electronic message from a message sender for routing to adestination address; establishing communication with an electronicmessage server associated with the destination address, the serverdefining a destination server; querying the destination server todetermine whether the destination server supports Delivery StatusNotification (DSN) functionality; receiving a response to the query, thequery and response together defining an SMTP dialog; requesting DeliveryStatus notification information from the destination server according toresults of the SMTP dialog; transmitting the electronic message to thedestination address; receiving DSN information from the destinationserver with respect to delivery of the electronic message; and providingto the message sender at least a portion of the SMTP dialog, and atleast a portion of the DSN information.

In yet another aspect, the invention is a method of verifying content ofa received electronic message, comprising: receiving the electronicmessage; generating a digital signature corresponding to content of thereceived message; providing the message and the digital signature to adesignated addressee; and, at a later time, verifying that the digitalsignature corresponds to the message.

In accordance with still another aspect of the present invention, themethod includes establishing whether a message was electronicallyreceived by a recipient, comprising: providing a message to bedispatched electronically along with a recipient's address from asender; creating a signature associating with the message; dispatchingthe message electronically to the recipient's address; tracking themessage to determine a final Delivery Status of the message dispatchedto the recipient's address; upon receiving final Delivery Status of themessage. generating a receipt, the receipt including a copy of themessage, the signature, and the final Delivery Status for the message;and providing the receipt to the sender for later establishing that themessage was electronically received by the recipient.

In accordance with yet another aspect of the present invention, a methodis provided for proving that an electronic message sent to a recipientwas read, comprising: providing an electronic message along with arecipient's address; calculating a digital signature corresponding tothe electronic message; dispatching the electronic messageelectronically to the recipient's address; requesting a Mail User Agent(email client “reading”) notification from the recipient: upon receivingthe reading notification, generating a reading receipt, the readingreceipt including a copy of the message, the digital signature for thecorresponding electronic message, and a second digital signature for thereading receipt from the recipient; and providing the reading receiptfor later verification that said message was received by the recipient.

In accordance with another aspect of the present invention, a method isprovided for validating the integrity of a purported copy of anelectronic message, comprising: receiving the purported electronicmessage copy, said purported copy including an encrypted message digestassociated therewith; decrypting the message digest; generating a secondmessage digest based on content of the purported copy; and validatingthe purported copy by comparing the decrypted message digest and thesecond message digest to determine whether the two message digestsmatch.

In accordance with a still further aspect of the present invention, amethod is provided for validating a received registered e-mail,comprising: receiving an electronic receipt, said receipt including abase message and an encrypted message digest; decrypting the encryptedmessage digest; generating a second message digest from the basemessage; and validating the e-mail if the decrypted message digestmatches the second message digest.

In yet another aspect, the invention is of a website at which users cango to send and receive secure messages, with the website host acting asan independent third party which will send and receive the messages andprovide secure documentation regarding the content and delivery of themessages.

The above-described objectives of the present invention and otherfeatures and benefits of the present invention will become clear tothose skilled in the art when read in conjunction with the followingdetailed description of a preferred illustrative embodiment and viewedin conjunction with the attached drawings in which like numbers refer tolike parts, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed description of the preferred embodiment of the invention willbe made with reference to the accompanying drawings.

FIG. 1 is a system diagram of a first embodiment of the presentinvention, in which outgoing messages are registered by beingtransmitted by a special Mail Transport Agent (MTA).

FIGS. 2A-2F constitute a representative flow diagram for registering anoutgoing e-mail according to the embodiment of FIG. 1.

FIG. 3 is a system diagram of a second embodiment of the presentinvention, in which senders may direct a Mail Transport Agent totransmit selected messages through a separate registering MTA.

FIG. 4 is a system diagram of a third embodiment of the presentinvention, in which carbon copies (cc's) of outgoing messages are sentto a special server to be registered.

FIG. 5 is a system diagram of a fourth embodiment of the presentinvention, in which users compose outgoing messages to be registered ata designated website.

FIG. 6 is a system diagram of a fifth embodiment of the presentinvention in which users may send registered e-mails and store receiptsfrom within a Web Based Mail User Agent (MUA).

FIGS. 7A and 7B constitutes a representative flow diagram for validatinga registered e-mail receipt.

FIG. 8 is a system diagram of an embodiment of the present invention forregistering incoming messages.

FIG. 9 is a flow diagram for registering incoming messages.

FIG. 10 is a flow diagram for validating received registered messages.

FIG. 11 is a system diagram showing an exemplary use of the presentinvention by an e-business to register and acknowledge incoming andoutgoing communications.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This description is not to be taken in a limiting sense, but is mademerely for the purpose of illustrating the general principles of theinvention. The section titles and overall organization of the presentdetailed description are for the purpose of convenience only and are notintended to limit the present invention. Accordingly, the invention willbe described with respect to e-mail messaging systems that use theInternet network architecture and infrastructure. It is to be understoodthat the particular message type and network architecture describedherein is for illustration only; the invention also applies to otherelectronic message protocols and message types using other computernetwork architectures, including wired and wireless networks. Forconvenience of discussion, messages that are processed according to thepresent invention may be referred to herein as being “registered”messages. In the discussion which follows, the term “RPost” will referin general terms to a third party entity which creates and/or operatessoftware and/or hardware implementing the present invention, and/or actsas a disinterested third party message verifier. The term is used forconvenience of exemplary discussion only, and is not to be understood aslimiting the invention.

I. RPost as Outgoing Mail Server Embodiment

FIG. 1 is a system diagram of a first embodiment of the presentinvention, wherein outgoing e-mails are registered according to thepresent invention. In this embodiment, the RPost registering server 14serves as the primary outgoing Mail Transport Agent (MTA) for a messagesender's Mail User Agent (MUA) 13. Although message recipient 18 istechnically the addressee and is therefore merely the intended recipientor intended destination at this point in time, for simplicity ofdiscussion this entity will be referred to herein as the recipient,addressee, or destination. Note that a single message may have manydifferent destinations and that each of these may be reached through adifferent MTA.

The method of sending registered messages may be divided into threeparts:

-   -   1) Preprocessing: Steps to be taken before a message is        transmitted;    -   2) Transmission: The method of delivering messages to        addressees;    -   3) Post Processing: Procedures for gathering information about        messages after their delivery, the creation of receipts, and the        validation of receipts.

1.1 Preprocessing

On receiving a message for transmission, the RPost server will createrecords in a database for each message that will be used to store suchinformation as:

a) the time at which the message was received;

b) the names of the attachments of the message;

c) the number of addresses of the message;

For each destination of the message the database will record:

a) the name of the destination (if available);

b) the Internet address of the destination;

c) the time at which the message was delivered to the destination's MailServer;

d) The Delivery Status of this destination:

Recipient Delivery Statuses used by the system will include:

-   -   UNSENT        -   This status indicates that the message has not been sent.    -   DELIVERED-AND-WAITING-FOR-DSN        -   This status indicates that the message has been delivered to            an ESMTP compliant MTA that supports Delivery Status            Notification (DSN) so that a success/failure notification            can be expected.    -   DELIVERED        -   This status signifies that the copy of the message sent to            this recipient has been successfully delivered to a server            that does not support ESMTP DSN.    -   DELIVERED-TO-MAILBOX        -   This status signifies that a DSN message has been received            which indicates that the copy of the message sent to this            recipient was delivered to the mailbox of the recipient.    -   RELAYED        -   This status signifies that an MTA DSN has been received            which indicates that the copy of the message sent to this            recipient has been relayed onward to another server.    -   UNDELIVERABLE        -   This status indicates that after repeated attempts RPost has            been unable to connect to an MTA to deliver the messages to            this recipient.    -   FAILED        -   This status signifies that an MTA DSN has been received that            indicates a failure to deliver a copy of the message to this            recipient.

At this time the system will also perform hashing functions on themessage's contents.

RPost server 14 employs a hash function and an encryption algorithm. Thehash function may be one of any well-known hash functions, includingMD2, MD5, the Secure Hashing Algorithm (SHA), or other hash functionswhich may be developed in the future. Hash algorithms and methods aredescribed in Bruce Schneider, Applied Cryptography: Protocols,Algorithms, and Source Code in C, John Wiley & Sons, Inc. (New York)1993; Federal Information Processing Standard Publication 180-1 (TIPSPUB 180-1) Secure Hash Standard, National Institute of Standards andTechnology; and U.S. Pat. No. 5,530,757 issued to Krawczyk, entitled“Distributed Fingerprints for Information Integrity Verification,” whichare hereby incorporated by reference for their teachings of hashfunctions, encryption, and methods and systems for implementing thosefunctions. Other known or new methods of detecting whether the contentsof the message have been altered may be used.

A good hash function H is one-way; that is, it is hard to invert where“hard to invert” means that given a hash value h, it is computationallyinfeasible to find some input x such that H(x)=h. Furthermore, the hashfunction should be at least weakly collision-free, which means that,given a message x, it is computationally infeasible to find some input ysuch that H(x)=H(y). The consequence of this is that a would-be forgerwho knows the algorithm used and the resulting hash value or messagedigest will nevertheless not be able to create a counterfeit messagethat will hash to the same number. The hash value h returned by a hashfunction is generally referred to as a message digest. The messagedigest is sometimes referred to as a “digital fingerprint” of themessage x. Currently, it is recommended that one-way hash functionsproduce outputs that are at least 128 bits long in order to ensure thatthe results are secure and not forgeable. As the current state of theart advances, the recommended length for secure hash functions mayincrease.

RPost server 14 computes a message digest for the message body, and aseparate message digest for each of the attachments of the message andstores these in a manner in which they may be later included in areceipt for the message.

Before the message is altered in the ways that registration willrequire, a copy of the original message and its attachments are storedin a manner in which they can be later retrieved by the system.

The RPost server may alter a message in several ways before transmissionto the recipient's MTA.

Although such is not necessary to the practice of the invention, themessage may be tagged to denote the fact that the message has beenregistered. such as by inserting the word “‘Registered” or at thebeginning of the “subject” line of the message, by appending a tag suchas:

-   -   “This message has been registered with RPost. Visit our web site        at www.RPost.com for additional information.”        at the end of the original message or other tagging.        Additionally, the tag may contain instructions, World Wide Web        addresses, or links that invite and allow the recipient to send        a registered reply to the message by linking to a Web Page from        which registered messages may be composed and sent.

Although tagging is optional, the delivered message will generally bereferred to herein as the tagged message.

Internet protocols provide two forms of receipt for e-mail messages:

MTA Notifications

-   -   These are e-mails that are sent by a recipient's MTA notifying        the nominal sender of the message that various events have        occurred. MTAs that conform to the SMTP protocol will typically        only send a notification in the event that the mailer cannot        deliver a message to the mailbox of the addressee (as might        happen if the address is not valid or if the addressee's mailbox        has exceeded its allotted storage quota).    -   With the introduction of the Extended SMTP standard it became        possible for sending MTAs to request notices of success and        failure in the delivery of messages. These Delivery Status        Notifications (DSNs) are e-mails which are sent by a receiving        MTA to the nominal sender of the message when certain events        occur: e.g. the message has been successfully deposited into the        mailbox of the recipient; the message cannot be delivered to the        recipient's mailbox for some reason; the recipient's message has        been relayed on to another server which does not give DSN        receipts.    -   Note that only e-mail servers that support the Extended SMTP        (ESMTP) protocol support this form of DSN and that support for        this function is optional for ESMTP servers and depends on the        configuration selected by the server's administrators.    -   Although DSN is a term that only came into use with the advent        of ESMTP, we will, in what follows, use ‘DSN’ to refer to any        MTA generated message relating to the status of a received        message whether or not it is in conformity to the ESMTP        protocol.

MUA Notices (Reading Notifications)

-   -   These are emails that are sent to the (nominal) author of a        message by the recipient's Mail User Agent (MUA) (e-mail        program) when certain events occur: e.g. the message is opened        for reading, or deleted from the system without being read. By        Internet convention (RFC 1891), no MUA program can be forced to        generate such notifications. Whether an MUA will generate these        receipts will depend upon the configuration chosen by its user.

The RPost server 14 will configure and transmit messages in a way thatattempts to elicit both MTA DSNs and MUA notices from compliant MTAs andMUAs. In order to elicit a Reading Receipt from compliant MUAs; certainheaders must be included in the header section of an e-mail message.Different MUAs respond to different headers; hence Server 14 will addseveral different headers to each message requesting a read notificationin a form recognized by various MUAs. These headers all take the form:

Header label: user name <user address>

For example:

Disposition-notification-to: john smith <jsmith@adomain.com> read-notification-to: john smith <jsmith@adomain.com>where ‘john smith’ is the name of the user to whom an MUA notificationis to be sent and ‘<jsmith@adomain.com>’ is that user's Internetaddress. Normally such headers would refer to the author of the messagebut in the case of the present method it is required that thenotification be returned to RPost so that the notification can beprocessed by RPost. To assure that this is so Server 14 will insertheaders that request that MUA receipts be sent to an address where theycan be processed by the RPost server, for example:“readreceipt@RPost.com.” This will direct any compliant recipient MUAsto send their notifications to an RPost address for processing.

The task of processing returned MUA notifications raises another problemthat must be dealt with at this stage. There are no standards governingthe format or content of MUA notifications. Often they will quote thesubject of the original message and the time of the event (e.g. “openedfor reading”) that they are reporting. But even if this information isincluded in the notification it is rarely sufficient to uniquelyidentify the message that prompts it or to identify the author of thatmessage. When the system receives a MUA notification it must be able toidentify the message that prompts it, so as to include the notificationinformation in the receipt that RPost will generate for the sender.Alternatively, the system must at least be able to reliably identify thesender of the message to which the MUA notification refers so that thenotification information can be passed on to the sender in the form ofan RPost Reading receipt (see below).

To accomplish the latter goal, the system can take advantage of the factthat Internet addresses have two components: a name field and an addressfield, where the address field is set off by corner quotes “< >”. MostMUAs will include both fields in the destination address of their MUAnotifications. In composing its requests for MUA receipts, the RPostsystem will include the Server 14 read receipt-handling address as theaddress for the notification but will use the address of the originalsender in the name field of the header. For example, where the originalsender of the message is user John Smith with Internet addressjsmith@adomain.com, the RPost server will include headers of the form:

Disposition-notification-to: jsmith@adomain.com readreceipts@RPost.com>

This will typically result in the compliant MUA sending a notificationto readreceipts@RPost.com addressed as:

jsmith@adomain.com <readreceipts@RPost.com>

On receipt of such a notification at the address“readreceipts@RPost.com,” the server can, by parsing the addressee'sfield; determine that the notification concerns a message originallysent by jsmith@adomain.com, even if this could not be determined by anyexamination of the contents of the notification. With this informationin hand, the server can then package the contents of the notification ina digitally signed RPost Reading receipt and send the receipt to theaddress jsmith@domain.com.

The RPost system will also endeavor to elicit and collect MTA DSNnotices generated by recipient MTAs. Since such notifications are alwayssent to the address listed in the “FROM:” field of the message header,server 14 must alter each message header so that the message is receivedas ‘*FROM:” an RPost address at which DSNs may be processed.

However the problem of processing DSNs raises another issue, which mustbe dealt with at this stage. DSNs do not have any standard content orformat; often it is impossible to determine, merely by examining thecontents of these e-mails, what message their contents are givingnotification of. This problem was supposed to have been addressed forDSNs generated in compliance with the ESMTP protocol by the use of DSNenvelope ID numbers (see RFC 1869). According to the protocol, atransmitting MTA can include a reference number along with its requestfor a DSN. This number would be quoted in any returning DSN, allowingthe sender to identify the subject message of the DSN. However, as amatter of fact, many MTAs that report themselves as supporting ESMTP DSNdo not return a DSN envelope ID or any other information sufficient toreliably identify the subject message. Finally, even where a DSN doesreturn information sufficient to identify the message it is givingnotice of, it often will not contain sufficient information to identifythe specific addressee of the message that has prompted thenotification. Thus, a single message might be sent to two addressees ata domain; one might be successfully delivered to the addressee'smailbox; the other, not. The MTA for the domain may report these eventsin a DSN in ways that provide no way for the recipient of the DSN todetermine which addressee was successfully delivered and which was not(as, for example, may happen if the DSN reports the recipient'saddresses as their local alias names rather than by the addressescontained in the original message).

The present invention solves this problem in four steps:

-   -   1) A unique identification number is generated for each outgoing        message (e.g. based upon a time stamp). This number is stored in        a database.    -   2) The recipients of each message are enumerated and the        identifying numbers are stored in a database.    -   3) The message is sent separately to each intended recipient's        MTA. (Even when two recipients have a common domain name and        MTA, the server will transmit the message to that MTA in two        separate SMTP telnet sessions.)    -   4) When Server 14 transmits the message to a recipient's MTA it        augments the message's “FROM” field to show the message as        having been sent from an address which incorporates the        message's unique ID and the identifying number of the sender.        The address also contains a substring (e.g. “rcpt”) that enables        the Server to identify return messages as DSNs.

Thus, a single message denominated “mmyyddss” by Server 14, from thesender named John Smith, might be sent to its first intended recipient(denominated “a” by the system) with a header reading:

From: John Smith <rcptmmddyyssa@RPost.com>

The same message would be sent to the second recipient with a headerreading:

From: John Smith <rcptmmddyyssb@RPost.com>

Many e-mail MUAs will only display the name of the sender of a messageand thus the special address will be unseen by most recipients.

The upshot of this form of addressing is that when the recipient MTAsissue DSNs (whether ESMTP compliant or not) they will address those DSNsto different RPost addressees. On receiving these DSNs, Server 14 canidentify them as DSN messages by their “RCPT” prefix and, by parsing theaddressees, can determine which message and which recipient is thesubject of the DSN.

System 14 will alter the ‘FROM’ field of each message to refer to arecipient of the message each time it attempts to transmit the messageto that recipient's MTA.

To insure that recipient replies to transmitted messages are directedproperly system 14 will add an explicit “reply-to:” message header intothe message listing the original sender's name and Internet address. Inthe case of the present example this would be:

Reply-to: john smith <jsmith@adomain.com>

This will lead recipient MUAs to address replies to a received messageto the actual sender's address, rather than the constructed RPostaddress.

1.2 Transmission

As noted above, it is part of the method that the RPost server transmitsa separate copy of an outgoing message to each addressee of thatmessage. Moreover RPost will attempt to make each such delivery througha direct SMTP connection with a mail eXchanger (MX) of record for eachdestination.

Note: Each valid Internet e-mail address includes an Internet domainname or IP address. Each domain name/address has associated with it ane-mail server(s) authorized to receive mail for addresses in thatdomain. It will be noted that some domains have more than one server.The Domain Name Server responsible for each domain broadcasts theidentity of its mail servers across the Internet. This information ispublicly available and is managed and transmitted in ways that conformto rules and conventions which govern Internet e-mail and Domain Nameservice.

Before transmitting a copy of a message to any destination the RPostserver will perform an Internet Name Server Lookup to identify an MTAassociated with the destination's domain. Having identified the MTAresponsible for receiving mail on behalf of a destination address, thesystem will attempt to open a telnet connection with the destination'slocal MTA.

It is common practice for Internet e-mails to be relayed from MTA to MTAuntil they reach their final destination. The primary purpose forrequiring a direct connection between the RPost server and thedestination's MTA is so that the RPost server can record delivery of themessage, (this record taking the form of an SMTP dialogue) with thee-mail server which has proprietary responsibility for receiving e-mailfor the recipient domain name.

The existence of this record provides helpful evidence that the messagewas delivered, in much the same way that a registered mail receiptprovides evidence of delivery. USPS Registered mail is treated asverifiably delivered if it can be proved to have been delivered to theaddressee's authorized agent (e.g. a secretary, or mail room clerk). Inthe event of any legal challenge to the evidentiary merit of an RPostdelivery receipt, it will be recognized that in selecting an Internete-mail service provider, the recipient has authorized that provider tocollect electronic messages on his behalf. In turn, that serviceprovider has acknowledged its status as the authorized agent for e-mailrecipients of that domain name by broadcasting the address of its MTAsas the receptive e-mail servers for this domain.

Accordingly, having delivered messages directly to the mail serverresponsible for receiving the recipient's e-mail, RPost will havedelivered the message to an agent the recipient has legally authorizedto receive his mail. By recording the delivery transaction (thattransaction taking the form of an SMTP dialogue) RPost can claim to haveproof of delivery to the recipient's authorized agent.

Note that while the method herein described attempts to collect otherforms of proof of delivery to each destination, whether or not theseattempts succeed will depend upon factors that. will not be in controlof RPost, (e.g. the form of SMTP support deployed on the recipient'smail server). On the other hand, every successful delivery direct to arecipient's mail server will always generate an SMTP record. Recordingthis record allows RPost to provide proof of delivery to any validInternet destination that complies with the minimum protocols (SMTP) forInternet mail. This represents an important advantage of the currentmethod over other methods that might attempt to prove delivery byreliance on ESMTP DSN.

Having identified the MTA for a destination of a message, the RPostserver will attempt to open an ESMTP connection with the destination MTAby issuing an “HELO” handshake in compliance with RFC 1869. If SERVER 16supports ESMTP, it will respond by listing which ESMTP services itsupports.

If SERVER 16 supports ESMTP, the RPost server will first determine ifSERVER 16 supports the ESMTP Service “VERIFY”. The Verify service allowsa calling SMTP server to determine, among other things, if an address inan MTA's domain is genuine. If the RPost Server determines by thesemeans that the address it is attempting to deliver its message to is notvalid, it will terminate the connection, cease attempting to deliver amessage to this addressee, and record, in its database, the status ofthis message destination as UNDELIVERABLE.

Whatever its result, the RPost Server will record the ESMTP VERIFYdialogue in a file and store it so that it may be later attached to orincluded in the Delivery Receipt for this message. It should be notedthat, out of concern for security, few ESMTP servers support the VERIFYfunction.

If System 16 does not support the VERIFY method, then the RPost serverwill nevertheless attempt to deliver the message to System 16. Typicallyan MTA will accept messages for any address nominally in its domain andwill later send a DSN if the address is invalid.

The RPost server will then attempt to determine if the destinationserver supports the ESMTP service DSN. If it does, RPost will transmitthe message with a request that SERVER 16 notify the sender of themessage with an ESMTP DSN if the delivery to the addressee succeeds orfails. After the successful transmission of the message to thisdestination the system will record the Delivery Status of thisdestination as DELIVERED-WAITING-FOR-DSN.

If Server 16 replies to the “HELO” handshake in a way that indicatesthat it does not support ESMTP, the RPost server will issue a “HELO”message to initiate an SMTP connection. If this connection is achieved,the RPost server will transmit the message in compliance with the SMTPprotocol and will record the Delivery Status of the destination asDELIVERED.

Whether the connection is SMTP or ESMTP, the RPost server will recordthe entire protocol dialogue between the two servers. Typically thisdialogue will include protocol messages in which, among other things,the destination server identifies itself, grants permission to upload amessage for a named recipient, and acknowledges that the message wasreceived. RPost will save the record of this transaction in such a waythat it may be later retrieved and included in or attached to the RPostDelivery Receipt for this message.

For various reasons RPost may not be able to achieve an SMTP connectionwith MTA of a recipient or it may achieve such a connection but bedenied permission to transmit the message by the recipient. In thatcase, if the Internet DNS lookup reveals that the destination address isserved by multiple MTAs, the RPost server will attempt to deliver itsmessage to each of these in turn. RPost will continue to attempt todeliver to an appropriate MTA as often as system resources permit. If,after a length of time, RPost cannot deliver the message to an address;it will mark the status of this recipient of this message as“UNDELIVERABLE” and stop attempting to send this message to thisdestination address.

When the RPost server succeeds in transmitting a message to adestination Server that explicitly supports ESMTP DSN, RPost will recordthe status of this recipient for this message as“DELIVERED-AND-WAITING-FOR-DSN”.

When the RPost server succeeds in transmitting a message to thedestination Server via a connection that does not explicitly supportESMTP DSN, RPost will record the status of this recipient for thismessage as “DELIVERED.”

I.3. Postprocessing

DSN Processing

MTA DSNs will be returned to the RPost Server addressed to fictitiousaddresses in its proprietary domain (e.g. “RPost.com”), these addresseshaving been constructed as described above. The RPost server will scanall inbound mail addressed to the domain and detect DSN messages bytheir identifying substring (e.g. “rcpt”). By parsing these addresses inthe manner described above, the system can identify the message and therecipient that has prompted the DSN notification.

There is no standard format for DSN messages; neither is there anystandard lexicon in which they report their results. To evaluate areceived DSN the system must look in the subject line and the body ofDSN messages for words and phrases that express the DSN's meaning. Forexample, such phrases as “successful delivery” or “delivered to mailbox”or “was delivered” normally signal that the message the DSN concerns wasdeposited to the mailbox of the destination. When it detects suchphrases the System will change the Delivery Status of this destinationof the message to “DELIVERED TO MAILBOX”.

Phrases such as “could not be delivered”, “fatal error”, “failure” and“unsuccessful” typically signal a DSN that reports a failure by the MTAto deliver the message to the destination. When it detects phrases suchas these in the DSN the system will change the record of the recipient'sDelivery Status to “FAILED”.

Though the system always delivers mail to a proprietary MTA for thedestination's domain, these MTAs will sometimes relay the message to adifferent server (as may be the case, for example; if the receiving MTAsends mail behind a firewall). In this case the DSN will contain suchphrases as “relayed” or “relayed onward”. In such cases the system willchange the recipient's Delivery Status to “RELAYED”.

Having evaluated the DSN and updated the recipient's Delivery Statusaccordingly, the system will save the DSN and any attachments it maycontain in such a way that this message(s) may be included in and/orattached to an RPost Delivery Receipt.

Message Management

From time to time the system will scan each sent message and examine thestatus of each destination of that message in order to determine if thesystem has completed processing of that destination's delivery. Thecriteria for completion depend upon the destination's Delivery Status:

-   -   DELIVERED: This status indicates that a copy of the message for        this recipient has been delivered to an MTA that does not        support ESMTP DSN. Such an MTA may nevertheless send a form of        Delivery Status Notification in the event that the message could        not be delivered to the Mailbox of the addressee (as might        happen, for example, if the destination address does not        correspond to a valid account within the domain). Accordingly,        the system will not treat the delivery for such a recipient as        completed until a period of time has elapsed since the delivery        to the recipient MTA. This time period-typically two to twenty        four hours—represents an estimate of the maximum time required        for a majority of servers to return a notification of a failure        to deliver and it may be adjusted if the specific destination        domain is remote or known to be prompt or tardy in producing        such notifications.    -   RELAYED: This status signifies that a DSN has been received that        indicates that the recipient MTA has forwarded the message to        another MTA that does not support ESMTP DSN. In this case it is        nevertheless possible that the MTA to which the message has been        delivered will send a notification of failure to deliver in due        course. Accordingly recipients with this status are treated as        complete under the same conditions as recipients with the status        DELIVERED.    -   DELIVERED-AND-WAITING-FOR-DSN: This status indicates that the        recipient's MTA supports ESMTP DSN and that a DSN has been        solicited but not yet received. It may sometimes happen that        although an MTA identifies itself as supporting this service it        will nevertheless not provide DSNs even in the event of        successful delivery. Accordingly, the system will regard        deliveries to a destination with this status as completed even        if no DSN is received after an interval of time. This        interval—typically six to twenty-four hours—represents an        estimate of the maximum time typically required for a compliant        MTA to return a DSN.    -   DELIVERED-TO-MAILBOX: This status indicates that a DSN        indicating successful delivery has been received for this        recipient and hence the delivery of the message to this        destination is completed.    -   FAILED, UNDELIVERABLE: Deliveries to recipients with this status        are always treated as complete.

When the system finds that delivery to all recipients of a message hasbeen completed the system will construct a Delivery Receipt for themessage.

Creation of Delivery Receipts

Delivery receipts are e-mails sent to the original sender of theRegistered message. The receipt 20 may contain:

-   -   1. an identifier for administrative purposes. This identifier        may be or may include reference to the sender's ID and/or the        value of the Internet Message-ID of the sender's message as        received by the system;    -   2. the date and time at which the receipt was generated;    -   3. the quoted body of the original message together with the        e-mail addresses of its intended recipients;    -   4. the date and time at which the RPost Server received the        message;    -   5. a table for each destination listing:        -   (i) the time at which the recipient's MTA received the            message and/or the time at which the system received a DSN            report from the recipient's MTA;        -   (ii) a Delivery Status of the message for that destination.            The Delivery Status quoted in a Delivery Receipt is based            upon the system's internal record of the destination's            Delivery Status. They may be transcribed as follows:            -   Deliveries to destinations whose status is FAILED or                UNDELIVERABLE will be recorded in the receipt as                “failed”.            -   Deliveries to destinations whose status is DELIVERED or                DELIVERED-AND-WAITING-FOR DSN will be recorded in the                receipt as “delivered to mail server”.            -   Deliveries to recipients whose status is DELIVERED                TO-MAILBOX will be recorded in the receipt as “delivered                to mail box”.        -   The purpose of these reports is to accurately apprise the            reader of the form of verification of delivery the system            has been able to achieve.    -   6. a list of the original attachments of the e-mail together        with the separate message digests of those attachments;    -   7. copies of the attachments to the original message, each        original attachment being attached as an attachment to the        receipt;    -   8. transcripts, summaries, or abstractions of the transcripts of        all of the SMTP dialogs involved in the delivery of the message        to each destination;    -   9. quotations from the bodies and the attachments of all        received DSN reports including whatever details of delivery or        disposition of the message that they might reveal; and    -   10. any files that were returned to the system as attachments to        DSN reports.

All of these separate elements of the receipt may have their own messagedigests or digital signatures included within the receipt. Additionally,the receipt may include a single overall encrypted message digest ordigital signature computed and appended as part of the receipt, thusproviding a single message authentication code which could be used toauthenticate all of the information contained within the receipt. Sincethe receipt itself and SMTP dialogs and DSN reports within the receiptcontain timestamps, the receipt includes a non-forgeable record of themessage recipient(s), the message content, and the time(s) and route(s)of delivery.

MUA Notification Processing

MUA Notifications could be collected and incorporated within RPostDelivery receipts in the same manner as MTA DSNs. However, MTAnotifications are typically issued by receiving MTAs within a few hoursof delivery whereas MUA Notifications will not be generated, if ever,until the recipient opens his MUA e-mail client and takes some actionwith respect to the received mail. For this reason, in this embodimentof the invention MUA notifications are collected separately from MTAnotifications and reported in “RPost Reading Receipts” separate fromRPost Delivery Receipts.

MUA notifications elicited by message headers constructed in the mannerdescribed above will be returned to a common RPost address (e.g.“readreceipts@RPost.com”) and each notification will contain—in the namefield of its address—the address of the original sender of this message.Because this is the only information required to generate an RPostreading receipt in the manner described below, the system can deal withMUA notices whenever these notices may arrive and without any need tohave stored any information about the original message in its databanks.

MUA notices may report, among other things, that a message has been readby a recipient. that a message has been displayed on the recipient'sterminal (whether or not read), that a message has been deleted withouthaving been opened. There is no protocol-governed standard for thecontent or format of MUA messages. The system could be configured so asto examine the text of MUAs to interpret their reports in the samefashion as the system uses for MTA DSNs. However, in the currentembodiment of the invention, MUAs are not evaluated or interpreted bythe RPost server but are, instead, passed on to the sender for his ownevaluation in a form that can be authenticated by RPost. To accomplishthis the system will create an e-mail message styled as an “R-PostReading Notice’” which may include, among other items:

-   -   1. subject line of the received MUA notice;    -   2. the body of the received MUA notice quoted as the body of the        Reading Notice;    -   3. the received MUA notice included as an attachment;    -   4. any attachment(s) to the received MUA notice included as an        attachment(s).    -   5. message digests of the received MUA notice and of any        attachment(s) to that notice;    -   6. a date and time stamp;    -   7. an encrypted hash of at least items 5 and 6 providing an        authenticatible date stamped digital signature for the document        and all of its contents.

Receipt Disposition

In the case of the current embodiment of the invention, both RPostdelivery receipts and Reading Notices are sent to the original sender ofthe registered message. Since these receipts are digitally signed withan encrypted hash, RPost can authenticate the information contained inthese messages any time they are presented to RPost for this purpose, inthe manner described below. This means that once it has transmitted acopy of the receipt to its sender (with instructions to the sender toretain the receipt for his records), RPost has no further need to retainany data concerning the message or its delivery and may expunge all suchrecords from its system. Thus, RPost need not keep any copy of theoriginal message or the receipt. This economy of archival memory givesthe present invention an advantage over various prior art messageauthentication systems that required large amounts of data storage atthe service provider side.

In this case the burden of retaining receipt data falls on the originalsender of the message. Alternatively or additionally, third partyverifier RPost may, perhaps for an additional fee, store a permanentcopy of the receipt or of some or all receipt data. The receipt orpart(s) thereof may be kept on any suitable archival storage devicesincluding magnetic tape, CD ROM, or other storage device types.Additionally or alternatively, RPost may return receipts or partsthereof to a storage system devoted to this purpose within the controlof the sender or the sender's organization.

As described above, RPost receipt information includes all of the datafrom the original sender's message and its attachments. There arecircumstances in which users of the system might not wish to undertakethe burden of retaining receipts in their records (e.g., out of fear ofaccidental data loss) but might also not wish to have the contents oftheir message in the hands of the RPost third party. Accordingly RPostmight discard the contents of messages but store in its database onlysuch information (e.g. sender, date of composition, message digests,destinations and Delivery Statuses) as might be required for RPost toauthenticate and verify the delivery of a message when presented with acopy of the message retained by the sender.

Verification

In the event that the originator of a message requires evidence at alater date that an e-mail was sent, delivered, and/or read, theoriginator presents the receipt(s) for the message to the operators ofthe system.

For example, in order to prove that a particular message was sent fromsender 10 to recipient 18, sender 10 sends to RPost a copy of receipt 20with a request to verify the information contained within the receipt.This could be done by sending the receipt to a predefined mailbox atRPost, e.g., verify @RPost.com. RPost then determines whether or not thereceipt is a valid receipt. A receipt is a valid receipt if the digitalsignature matches the remainder of the receipt, and the message digestsmatch the corresponding respective portions of the original message.Specifically, RPost performs the hash function on the various portionsof the message including the message body, the attachments, and theoverall message including the SMTP dialog and DSN reports, to produceone or more message digests corresponding to the purported message copy.RPost compares the message digests in the purported copy, including theoverall message digest, with the message digests which RPost hascomputed from the purported message copy. The overall message digest canbe compared by either decrypting the overall message digest received asthe digital signature in the purported receipt, or by encrypting theoverall message digest which was calculated from the purported messagecopy. If the message digests including the digital signature match, thenthe receipt is an authentic RPost-generated receipt. Assuming that agood hash function was used and that the keys used in the cryptographichash function and the digital signature encryption algorithm have notbeen divulged to others, it is virtually impossible that the receipt hasbeen “forged” by the person presenting the receipt. That is, the receiptmust have been a receipt that was generated by RPost, and therefore themessage contained in the receipt, the to/from information, the date andtime of delivery, the fact of successful delivery, the route by whichthe message traveled, and any DSN information contained within thereceipt, must be a true copy of that information and is accurate. RPostcan then provide authentication, verification, and confirmation of theinformation contained within the receipt. This confirmation can take theform of an e-mail confirmation, affidavit testimony from RPost employeesfamiliar with the methods used by RPost, live sworn testimony indepositions and in court, and other forms of testimony. RPost can chargesender 10, recipient 18, or any other entity, fees for the variousrespective confirmation services. RPost can also provide testimony orother confirmation with regard to the nonauthenticity of a purportedreceipt. Testimony may be provided in accordance with Federal Rules ofEvidence 901(9). 901(10), 803(6), 803(7), 1001-1004, 1006, 702-706,corresponding state rules of evidence, and other applicable rules.

In sum, the system provides reliable evidence based on the testimony ofa disinterested third party that a particular message having aparticular content was sent, when it was sent, who sent it, who receivedit, when it was opened for reading, and when it was deleted. Thisevidence can be presented any time a dispute arises regarding thecontent and delivery of messages, as for example in contract formation,the timing of stock buy or sell orders, and many other applications. Theoperators of the system can attest to the accuracy of the informationcontained in the receipt itself without the need for the operators topreserve any record or copy of the information contained in the receipt.

A significant advantage of the system is that it can be used by existingMUAs without any change thereto. Because all the computation,encryption, ESMTP interrogation and dialog, DSN report collection, andreceipt compilation, are performed by the third party RPost server, noneof these functions need to be implemented within any of the user'sequipment. Thus, users can take advantage of the system quickly andeasily.

In the embodiment of the invention described above, the RPost Serverregisters the delivery of all messages passing through it.Alternatively, an RPost server might register only those messages havingcertain destinations (e.g. external to an organization) or from certainsenders (e.g. a customer relations group). Alternatively oradditionally, the RPost server might register only those messages thathad distinguishing characters or strings in the subject or body of themessage. For example, the server might register only messages that thesender had included “(R)” in the subject of the message. All othermessages might be delivered by the RPost Server or some other serverfunction as an ordinary Internet MTA.

In this embodiment; RPost can raise revenue in a variety of ways. Forinstance: RPost can charge message sender 10 or her organization a feeon a per-message basis, on a per-kilobyte basis, on a flat fee periodicbasis such as monthly, or on a combination of the above. RPost can alsocharge fees for authenticating and verifying a receipt, with a scheduleof charges depending on whether the verification sought is a simplereturn e-mail, a written affidavit or declaration, sworn fact testimonyin deposition or in court, or sworn expert testimony in deposition or incourt. If the users opt to have RPost retain copies of the receipts,RPost can charge per item and/or per-kilobyte per month storage fees.

II. Flow Diagram for Registering an Outgoing Message

FIGS. 2A-2G constitute a flow chart showing an exemplary operation ofthe first embodiment of the system. Modifying this flow chart to applyto other embodiments is within the skill of one familiar with softwareand e-mail protocols.

FIG. 3A, Pre-processing, illustrates the steps taken with a messagebefore it will be transmitted by the Registering Server (the System).

To register an e-mail message, in step 201 an originator/sender/usercreates an email message using any Internet Mail User Agent (MUA).Possible MUAs include: (1) client side e-mail programs; (2) server basede-mail programs; (3) web based e-mail services; and (4) HTML formssubmitted through web pages. The message may contain attached files asdescribed in the Requests for Comments (RFCs) 822, 2046, and 2047, whichare hereby incorporated by reference. RFCs are a series of notesregarding the Internet that discuss many aspects of computercommunication, focusing on networking protocols, procedures, programs,and concepts.

In this embodiment, the system functions as the sender's outgoing mailserver and hence the sender's message will be directly transferred tothe RPost Server by the sender's MUA (step 202).

In step 203, the system creates a copy of the original message to bestored for later processing.

In step 204, the system creates a record in a database which may includesuch information as: the time at which the message was received by theserver, the names and size(s) of the file attachment(s) of the message,the name (if known) of each destination of the message; the Internetaddress of each destination; the time at which the message was deliveredto the destination's MTA (initially this value is null) and a unit whichrecords the Delivery Status of each destination.

In step 205, the Delivery Status of each destination is set to “UNSENT”.

In step 206, the system generates and stores a message digest or digitalfingerprint generated from the message body.

In step 207, the system generates and stores a hash or message digestfor each attachment included in the message.

In step 208, the system may create a modified copy of the originalmessage. In this second copy (step 209), the original subject line ofthe message may be amended to indicate that this copy is registered(e.g. by pre-pending “Registered”).

In step 210, a notice that the message is registered by the systemtogether with links to the system's Word Wide Web site may be appendedto the body of the message.

In step 211, the e-mail headers may be added requesting readingnotification in a variety of header formats recognized by various MUAs.The requests for notification direct the return notification to anaddress associated with the system: for example,“readreceipt@RPost.com”. These headers will also include the address ofthe original sender of the message in the name field of the address towhich the MUA notification should be sent.

Preprocessing having been completed, the system will now transmit a copyof the message to each of its destinations as illustrated in FIG. 2B.

FIG. 2B illustrates the steps required to transmit a registered message.As step 220 indicates, the process requires a separate transmission foreach recipient of the message.

In step 221, the system changes the header field of its working copy ofthe message to show the message as being “FROM:” a sender whose name isthe original sender of the message but whose address is an “RPost.com”address constructed from:

-   -   a) a string used to identify returning MTA notifications (e.g.        “RCPT”);    -   b) a string which uniquely identifies the message being sent;    -   c) a tag which uniquely identifies the destination this copy of        the message is being sent to.

In step 222, using the domain name of the destination currently beingsent to, the system does a Domain Name Server Mail exchange lookup tofind the address of the MTA(s) responsible for collecting mail foraddresses in this domain.

In step 223, the system attempts to make a direct telnet connection tothe MTA of the destination. If the connection fails, the system will tryto make the connection again. Provided that the system has not exceed amaximum number of retries (227) for this destination, the system willtry to remake the connection perhaps using another MX server for thedestination's domain (228).

If, after a maximum number of retries, the system cannot connect to anMTA for this destination, the system will, as in step 226, record thisdestination's Delivery Status as “UNDELIVERABLE” and cease attempting todeliver this message to this destination.

On connecting to the destination's MTA, the system will begin making arecord of its (E)SMTP dialog with the MTA (225).

In step 229, the system attempts to initiate an Extended SMTP (ESMTP)exchange with the destination MTA by issuing an “HELO” greeting.

If the destination's MTS supports ESMTP, the system will then (230)determine if the destination MTA supports the SMTP function VERIFY. Ifthe MTA supports VERIFY, the system will attempt to determine if thedestination address is a valid address within the domain (231).

If the address is not valid, then, as in step 232, the system willrecord the Delivery Status of this destination as “FAILURE” and willcease attempting to deliver this message to this destination.

If the address is valid or if the ESMTP server does not support VERIFY,the system will then (233) determine if the receiving MTA supports theESMTP service DSN (Delivery Status Notification).

If the MTA does support ESMTP DSN, the system will transmit the messagewith ESMTP requests to notify the nominal sender of the message ofdelivery success or failure (234). Having transmitted the message, thesystem will record the Delivery Status of this destination as“DELIVERED-AND-WAITING-FOR-DSN” (235).

If the receiving MTA does not support Extended SMTP, the system willtransmit the message using SMTP (236) and record the destination'sstatus as “DELIVERED” (237).

Having delivered the message, the system will then store the (E)SMTPdialog, recording the delivery in a manner in which it can later berecovered (238) and attempt to send the message to another destination.

Having transmitted a message to its destination(s), the system mustperform several functions in order to gather information about themessage's disposition. FIG. 2C illustrates the process by which thesystem processes MTA Notifications returned by recipient MTAs.

Because of the format used in the headers of sent messages illustratedin FIG. 2B step 221, MTA message notifications will be delivered to afictional local address at the server. The system will be able to detectthese notifications by a string (e.g. “rcpt” embedded in their addresses(241). By parsing the address, as illustrated in 242, the system candetermine which message to which destination prompted the receivednotification.

In step 243, the system scans the subject line and the body of receivedMTAs for phrases that indicate whether the MTA is reporting a successfuldelivery, a failed delivery, or that the message has been relayed toanother server.

In the event that the process at step 243 reveals that the notificationis reporting a successful delivery, the system will, as illustrated instep 245, change the Delivery Status of the relevant destination of therelevant message to “DELIVERED-TO-MAILBOX”.

If the system determines that the MTA notice is reporting a deliveryfailure, the system will (247) change the Delivery Status of therelevant destination of the relevant message to “FAILURE”.

In the event that the system determines that the MTA notificationindicates that the message was relayed to another server, the systemwill, as illustrated in step 249, change the Delivery Status of therelevant destination of the relevant message to “RELAYED’”.

Having processed the MTA Notification, the system will save this messageand all of its attachments in such manner that they may be laterrecalled and used in construction of a receipt for this destination(250).

From time to time, as illustrated in FIG. 2D, the system will examinethe status of each message to determine if the system has recovered allof the MTA notifications it is likely to receive for each destination ofmessage and may hence proceed to construct a receipt for the message.

The system will examine the Delivery Status of each destination of themessage.

If any destination has the Delivery Status “UNSENT”, then the processingof the message is not complete. (252).

If the Delivery Status of a destination is “DELIVERED-AND-WAITING-FORDSN”, then the system will not regard the processing for thisdestination as complete unless, as is illustrated in step 254, the timesince delivery of the message has exceeded the system's waiting period(e.g. 24 hrs.).

If the Delivery Status of a destination is “DELIVERED”, (257) then thesystem will regard the processing of this destination as completeprovided (258) that a period of time has elapsed which the operators ofthe system treat as sufficient to have received notice of deliveryfailure from the destination's MTA. (e.g. 2 hours).

Any other destination Delivery Status (e.g. “FAILED”, “UNDELIVERABLE”,“DELIVERED TO MAILBOX”) is treated as having completed processing.

If processing of any of a message's destinations is not complete thesystem takes no action but moves to consider other messages in thesystem (step 255).

However; as illustrated in step 259, if processing of every destinationof the message is complete, the system will generate a Delivery Receiptfor the message.

As illustrated by way of example in FIG. 2E, the receipt may include:

-   -   An identifier for administrative purposes as in block 271. This        identifier may be or may include reference to the sender's ID        and/or the value of the Internet Message-ID of the sender's        message as received by the system.    -   As in block 272, the quoted body of the original message 12        together with the e-mail addresses of its intended recipients        may also be included.    -   As in block 273, a table for each recipient listing may include:        -   the time at which the recipient's MTA received the message            and/or the time at which the system received DSN from the            recipient's MTA;        -   the Delivery Status report of the message for that            destination, i.e., “Delivered to Mail Server”, “Delivered to            Mail Box”, “Relayed”, “Delivery Failure”, “Undeliverable”;    -   As in block 274, a list of the original attachments of the        e-mail together with their separate hash values or message        digests.    -   As in block 275, transcripts or abstractions of the transcripts        of all of the SMTP dialogs involved in the delivery of the        message to each destination.    -   As in block 276, quotations from the bodies and the attachments        of all received DSNs including whatever details of delivery or        disposition of the message that they might reveal.    -   As in block 277, the system may attach to the receipt copies of        all of the attachments of the original message, and, as in block        278, the system may additionally attach files returned to the        system as attachments to DSNs.

In step 279, having generated the text of the receipt so far, the systemthen generates a first hash for the e-mail message and a second hash(es)for any attachments to the body of the receipt and calculates a digitalsignature for each of the hash(es) using an encryption key known only tothe operators of the system. Encryption can employ, for example, theData Encryption Standard described in Federal Information ProcessingStandard Publication 4-2 (FIPS PUB 46-2), the Data Encryption Standard,National Institute of Standards and Technology, which is herebyincorporated by reference. Alternatively, other known or new methods ofencrypting the hash value may be used.

In step 280, the encrypted hash is then appended to the end of themessage as the “document digital signature”.

In step 281, the receipt 20, now being complete, may be sent by e-mailto the sender with the advice that it be kept for the sender's records.

In step 282, the system may now delete all copies of the originalmessage, attachments, and DSNs. Alternatively, rather than sending thereceipt to the sender, the system may store the receipt, or both thesender and system can store the receipt.

Because MUA notifications are returned only at the option of therecipient and only when the recipient takes some action with respect tothe received message, embodiments of the system may choose to treatthese return messages differently than MTA notifications.

FIG. 2F illustrates how these MUA notifications may be treated by thesystem. MUA notifications are solicited by the system by includingvarious headers in outgoing messages in the manner of FIG. 2A, step 211.These headers direct compliant MUAs to send notifications to a systemaddress (e.g. readreciept@RPost.com”) set aside for this purpose. Theheaders also use, in the “name” field of this return address, the e-mailaddress of the original sender of the message. Accordingly, in step 286,when MUA notifications are returned to readreceipta,RPost.com the systemcan, by examining the address of the notification, determine the addressto which a reading notification should be sent.

Upon the arrival of a read receipt from a destination's MUA, the system,in step 287, generates a reading receipt that contains the subject ofthe received MUA notification as its subject and incorporates, in itsmessage body, the body of the received MUA Notification.

In step 288, the system attaches to the receipt any files that mayaccompany the MUA's receipt (typically these may include details ofdelivery or disposition and identifying references to the originale-mail.)

In step 289, the system generates a hash for any files attached to thereceipt and records this hash in the body of the receipt.

In step 290, the system generates a hash for the body of the receipt andits attachments, encrypts this hash, and appends the result to themessage as a “document digital signature”.

In step 291, the system sends the resulting receipt to the sender of themessage. In step 292, having sent this receipt, the system may deleteall internal records of the transaction.

III. RPost as Secondary Mail Server Embodiment

FIG. 3. is a system diagram of a second embodiment of the presentinvention wherein the RPost server does not serve as the user's primaryMTA but rather works in collaboration with another MTA. In thisembodiment, the sender may elect to register a particular outgoingmessage by including some form of flag in an outgoing message, messagesubject, or message addresses. For example, if and only if a senderincludes the symbol “(R)” in the subject of the message the sender's MTAwill direct the message to be transmitted through the RPost server togenerate a receipt.

In this embodiment the operators of RPost receive revenues from theoperator of the sender's MTA per message and/or per kilobytetransmitted.

IV. CC to RPost Embodiment

FIG. 4 is a system diagram of a third embodiment in which a carbon copy(“cc”) is sent to the RPost server. In this embodiment, the user ormessage sender 10 can use a standard MUA and standard MTA withoutmodification. Message sender 10 composes the e-mail having a messagebody and any number of attachments, and addresses it to messagerecipient 18, along with any carbon copies (cc's) and blind carboncopies (bcc's) as desired. Additionally, message sender 10 addresses acc to RPost. RPost server 14 tags the message as before, and sends thetagged message including attachments to the recipient's MTA 16 and anydesignated cc's. On receipt of such a copy RPost Server 14 may send ane-mail acknowledging receipt of the copy.

Recipient 18 and other destinations of the message will now receive twoversions of the same message: a first version of the message receiveddirectly from sender 10, and a second and tagged version which wasforwarded from RPost. Once RPost receives confirmation from recipientMTA 16 that the tagged version of the message was successfully receivedby recipient MTA 16, RPost server 14 composes message receipt 20 asbefore and sends the receipt to sender 10 for his records.

Revenue can be generated by establishing accounts for messageoriginating domains or individual message senders, and charging theusers' accounts per message, per kilobyte, per month, or a combinationof these. Revenue can also be generated for the placement ofadvertisements on receipts and from authentication and verificationservices as previously described.

V. Website Embodiment

FIG. 5 is a system diagram of a fourth embodiment. In this embodiment,RPost server 14 is associated with a website at which a user composesmessages. Message sender 10 visits the RPost Website and composes hismessage at the website by entering the desired “to”, “cc”, “bcc”,“Subject”, and message text information. Attachments can be added byusing features available on standard browsers and web servers. In thisembodiment, the sender must additionally provide an address to which theregistration receipt may be sent. RPost server 14 sends the receipt tosender 10 through sender's MTA.

Revenue can be generated by establishing accounts for messageoriginating domains or individual message senders, and charging theusers' accounts per message, per kilobyte, per month, or a combinationof these. Revenue can also be generated for the placement ofadvertisements on receipts and from authentication and verificationservices as previously described.

VI. Web Based MUA Embodiment

FIG. 6 is a system diagram of a fifth embodiment. In this embodiment,the RPost server 14 is associated with a web based Mail User Agent. Inaddition to allowing users to compose mail through a web browser, suchan MUA provides subscribers with browser viewable mailboxes that displaymessages stored on the Web server site. Subscribers to such a servicegain access to mail accounts with usernames and passwords. In thisembodiment, message sender 10 visits the RPost Website, accesses a WebBased e-mail account by entering a username and password, and composeshis message which is transported for delivery to RPost Server 14.Receipts generated by the RPost server are returned to a web basedmailbox associated with the subscriber's account.

In addition to the revenue sources available in other embodiments, inthis embodiment the operators can charge storage fees for receipts heldin the web based mailbox.

In all of these embodiments, the receipt may serve as evidence that:

-   -   (1) the originator sent an e-mail message;    -   (2) the message was sent at a certain time;    -   (3) the e-mail was addressed to certain recipient(s); 37    -   (4) the e-mail was delivered to the e-mail mailbox of each of        its intended recipient's);    -   (5) the e-mail was delivered at a certain time;    -   (6) the e-mail was delivered by a certain network route; and    -   (7) the e-mail message and its attachments had the specific        content recorded in the receipt.

Furthermore, the system under certain circumstances generates a separatereceipt, which may be used as evidence that:

-   -   (1) the e-mail was inspected through the recipient's Mail User        Agent (MUA); and    -   (2) the recipient took certain actions in response to the        message, e.g., read or deleted the e-mail, at a particular time.

As with the other embodiments, this embodiment produces documentedevidence which may be attested to and verified by the disinterestedthird party operators of the system of the delivery and integrity of anelectronic message. In other words, the system can be thought of astransforming the e-mail to a registered e-mail that can later be used toprove that a particular e-mail message was sent, that it wassuccessfully delivered, and when and how.

Should a dispute ever arise, the dispute can be resolved through thereceipt generated by the system because the receipt is so encoded thatthe operators of the system can determine the authenticity of thereceipt as the product of the system. Thereafter, operators of thesystem can attest to the accuracy of the information contained in anauthentic receipt, relying only on information contained in the receiptitself and without the need for the operators to preserve any record orcopy of the information contained in the receipt.

In addition to these benefits, the receipts generated by the system mayalso be useful as evidence of the existence and authorship of suchmaterials as might be transmitted through the system. Moreover, thesystem is easy to use, as the system can be used from any Internete-mail client program/MUA, so that there is no additional softwarerequired.

Flow Diagram for Validating a Receipt

FIGS. 7A and 7B constitute a flow diagram illustrating an exemplarymethod for validating a receipt. In the event that the sender of amessage should require evidence that an e-mail was sent and delivered(and/or read) the sender presents the receipt(s) corresponding to themessage to the operators of the system in step 700. The operators of thesystem then, in step 702, detach and decrypt the document digitalsignature appended to the receipt. In step 703, the operators generate ahash of the balance of the document, including attachments.

In step 704, if the current hash value does not match the decrypted hashvalue, then the system generates a report stating that RPost cannotauthenticate the receipt as an accurate record of the delivery or thecontents of the message described in the receipt.

If the decrypted hash is equivalent to the current hash of the message,the system can, as in step 706, warrant that the information containedin the body of the message is unchanged since the receipt passed throughthe system. If the original message contained no attachments, the systemmay now generate a report that warrants that the receipt is an accuraterecord of the message's contents and its delivery by the RPost Server.

If the receipt reports that the original message contained attachments;then the receipt will also record the name and hash value of eachattachment. In generating the receipt all attachments of the originalmessage are attached unchanged to the receipt. Accordingly, the systemwill, for each such attached file, generate a hash of the attached file(708) and compare it to the hash value recorded in the body of thereceipt (709).

If the calculated hash value of a file matches the value included in thereceipt, the system can warrant that the file attached to the receipt isidentical to that attached to the message as originally delivered. Ifthe hashes do not match, then the system will report that it cannotwarrant that the file attached to the receipt is identical to the fileattached to the original message.

Having performed this calculation for each file attached to the originalmessage, the system prepares a report which reports on the authenticityof the receipt and each of its attached files (710) or which reports thefailure of validation (712).

Having completed its evaluation, the system will then append a copy ofthe receipt and all of its attachments to the report it has generatedand send it via e-mail to the return address of the user who submittedthe report for validation.

VII. Registering Inbound E-Mails

FIG. 8 is a system diagram illustrating another embodiment of theinvention in which incoming e-mails are registered. In this embodiment,a message sender 60 sends an e-mail message 70. Sender's MTA 62 sendsmessage 70 onto the Internet as usual. However, in this embodiment RPostcontracts with service subscriber/recipient 68 to register incominge-mails. According to the agreement, RPost is designated with NetworkSolutions, Inc. (NSI) or other domain name authority as the mailrecipient (MX server) for recipient 68. This causes the Domain NameService (DNS) request performed by the sender's MTA 62 to return the IPaddress of RPost as the IP address for the recipient, which in turncauses sender's MTA 62 to send the e-mail message to RPost server 64.RPost server 64 acts as an SMTP, POP, POP3 or IMAP MTA (collectively,“POP mail server”) for recipient 68. SMTP, POP and IMAP MTAs aregoverned by RFC 821, the SMTP protocol, RFC 1939 Post OfficeProtocol—Version 3 (which obsoleted RFC 1725), and RFC 2060 IMAP(Internet Message Access Protocol) Version 4 rev 1 (which obsoletedRFC1730), which are hereby incorporated by reference.

RPost Server 64 prepares a registered version 74 of the original message70, and places this registered version 74 into recipient 68's in-boxinstead of, or in addition to, the original message 70. The registeredversion may have all of the verification and informational features andoptions discussed earlier in connection with e-mail receipts. Thisinformation can include, but is not limited to: individual messagedigests for each of the message body and text, the to/from information,other header information, each attachment, an overall message digest anddigital signature and message routing information and tags. Registeredversion 74 of message 70 as shown in FIG. 6 includes the message bodyincluding the header information, an attachment, separate messagedigests for each, and a digital signature or encrypted message digest.The hash functions and encryption are performed using private phrases orprivate keys known only to the operators of the system. The registeredversion 74 is made available to recipient 68 for inspection ordownloading through the recipient's MUA.

RPost server can optionally send a confirming e-mail 72 to messagesender 60. Confirmation message 72 can be a simple text messageindicating that a message was received and registered. Confirmationmessage 72 could also include a message such as. “Your e-mail messagewas received on Mar. 24, 2000 at 2:05 p.m. The digital signature of themessage was [128-bit digital signature]. For more information, visit ourwebsite at www.RPost.com.” Alternatively, or additionally, confirmationmessage 72 could include all of the information contained in theregistered version 74.

Thus, the system may provide to message recipient 68 a receipt 74 orother verifiable confirmation that:

-   -   (1) the recipient received an e-mail message;    -   (2) the message was received at a certain time;    -   (3) the e-mail was addressed from a certain sender;    -   (4) the message purports to be delivered via a certain network        route; and    -   (5) the e-mail message and its attachments had a specific        content.

Accordingly, the system provides evidence, which may be attested to bythe operators of the system, that particular electronic messages anddocuments were delivered to recipients having certain content andrepresenting themselves as having come from certain senders.

FIG. 9 is a flow chart illustrating one example of registering in-boundmail. In step 901, RPost server 64 receives a new e-mail message. Instep 902, the system generates a hash/digital signature of the message'scontents including the message's headers and attachments. Additionally,the system may generate a separate hash for each message attachment. Instep 903, the system encrypts the hash(es) using an encryption key knownonly to the operators of the system. In step 904, the resultingencrypted hash(es) is then appended to the body of the message. Then, instep 905, the modified message may be made available for inspection ordownload through the recipient's MUA.

FIG. 10 is a flow chart of one example of validating a receivedregistered e-mail message. In step 1000, in the event that the recipientof a message should require evidence that an e-mail with a specificcontent was received at a particular time, the recipient can present acopy of the registered version 74 (FIG. 8) of e-mail message 70 to theoperators of the system for verification. To verify the message, in step1001 the system detaches and decrypts the document digital signatureappended to the message. In step 1002, the system generates a hash ofthe balance of the document, and one for each file attached to themessage. In steps 1003 and 1004, the hashes are compared. If thedocument hash(es) matches the decrypted hash(es), then the message andits attachments must have passed through the system and have not beenaltered since their delivery to the 5 recipient.

Having determined that the e-mail is unaltered, the operators of thesystem can warrant that:

-   -   (1) the e-mail was received by the system at a certain time;    -   (2) the e-mail purported to arrive at the system via a certain        Internet route;    -   (3) the e-mail purported to be from a certain sender; and    -   (4) the e-mail and its attachments were delivered with. the        specific content they currently contain.

On the other hand, in step 1006, if the hash values do not match, thenthe operator cannot warrant that the e-mail is authentic, i.e., that thee-mail is an accurate version of an e mail that was received by thesystem.

FIG. 11 illustrates how the invention may be used by a business whichutilizes electronic tools (an “e-business”). An e-business 30 canutilize the system to register all incoming and outgoing e-mail messagesfrom its customers 34. In this case, the system includes Post OfficeProtocol (POP) server 36 and Simple Mail Transfer Protocol (SMTP) server38. For example, the e-business 30 can set up its website to e-mailforms to customers, and to forward queries and complaints 40 fromcustomers 34. The registered queries, complaints, orders; offers topurchase, and other information 46 are sent to the e-business 30 by thesystem. Receipts are then provided to the customers 34 via SMTP server38. This way there is no question regarding whether or not the customersent the communication and what it contained. Moreover, the e-businesscan set up a web site 32 through the RPost server so that everycommunication with the customers can be registered. In other words,through the web site form data orders 42 and automated responses 44 canbe registered through the system server; furthermore, any confirmation,collections notices, customer support, and special offers 48 sent by thee-business to customers 34 can be registered and the confirmation sentto the customer to eliminate arguments about what was ordered, when, orby whom. If desired, identical receipts can be provided to both thecustomers 34 and to e-business 30. Alternatively, the functions of POPserver 36 and SMTP server 38 may be combined in a single system server.

POP is a protocol used to retrieve e-mail from an e-mail server. Manye-mail applications (sometimes called e-mail clients) use the POPprotocol, although some can use the newer Internet Message AccessProtocol (IMAP). One version of POP, called POP2, requires SMTP to sendmessages. A newer version, POP3, can be used with or without SMTP. SMTPis a protocol for sending e-mail messages between servers. Many e-mailsystems that send e-mail over the Internet use SMTP to send messagesfrom one server to another; the messages can then be retrieved with ane-mail client using either POP or IMAP. In addition, SMTP is generallyused to send messages from a mail client to a mail server. E-mailservers may use a variety of protocols to communicate with the Internet.Commonly used protocols include SMTP, POP3 and IMAP4. Mail readers areat the opposite end of the server. Since mail servers receive messagesvia SMTP, e-mail readers send e-mail to a mail server using SMTPLikewise, since mail servers send messages using POP3 and optionallyIMAP4, mail readers receive messages from mail servers by using the POP3or IMAP4 protocol.

Although the above generally describes a system and method of verifyingthat an e-mail was sent and/or received, the present invention may applyto any electronic message that can be transmitted through an electronicmessage network or through any electronic gate. Electronic messages mayinclude text, audio, video, graphics, data, and attachments of variousfile types. The methods and techniques taught herein can be programmedinto servers and other computers, and computer programs implementing theinvention can be written onto computer readable media including but notlimited to CD ROMs, RAM, hard drives, and magnetic tape. E-mailregistration services according to the present invention can be bundledwith Internet service provider (ISP) services to provide a singleprovider ISP solution to corporate and other institutional clients.Implementing the above-described invention is within the skill of theordinary practitioner of the software arts.

Although the present invention has thus been described in detail withregard to the preferred embodiments and drawings thereof, it should beapparent to those skilled in the art that various adaptations andmodifications of the present invention may be accomplished withoutdeparting from the spirit and the scope of the invention. Accordingly,it is to be understood that the detailed description and theaccompanying drawings as set forth hereinabove are not intended to limitthe breadth of the present invention, which should be inferred only fromthe following claims and their appropriately construed legalequivalents. In the following claims, those claims which contain thewords “means for” are intended to be interpreted in accordance with 35U.S.C. §112, paragraph 6; those claims which do not include the words“means for” are intended to not be interpreted in accordance with 35U.S.C. §112, paragraph 6.

What is claimed is:
 1. A method of transmitting a message from a senderto a recipient through a server displaced from the recipient, the stepsat the server comprising: receiving the message at the server from thesender; transmitting the message to the recipient; receiving at theserver at least a portion of a data transport protocol dialog generatedduring transmission of the message from the server to the recipient; andreceiving at the server from the recipient an indication of the successor failure to deliver the message to the recipient; forming at theserver a first information from the at least a portion of the datatransport protocol dialog and the indication of the success or failureto deliver the message by the recipient; and transmitting, before anyauthentication of the message, a copy of the first information to thesender from the server.
 2. The method of claim 1, wherein the copy ofthe first information is stored in a memory in communication with theserver.
 3. The method of claim 1, wherein transmitting, before anyauthentication of the message, includes transmitting a copy of themessage and the first information to the sender from the server.
 4. Themethod of claim 1, further comprising: receiving a request from thesender to the server to authenticate the message; receiving the firstinformation and a copy of the message from the sender before anyauthentication of the message by the server, after the sender requeststhe sender to authenticate the message; and processing at the server thefirst information and the message without any assistance from therecipient to authenticate the message.
 5. The method of claim 4, whereinprocessing the first information to authenticate the message includesgenerating a written report containing information regardingauthenticity of the message.
 6. The method of claim 1, wherein the firstinformation is an authenticatible information which also includes aplurality of digits in a unique sequence.
 7. The method of claim 1,wherein transmitting a copy of the message and the first information tothe sender includes also sending a time of transmission of the messageto the recipient to the sender.
 8. The method of claim 1, wherein themessage received by the server is a copy of a message transmitteddirectly from the sender to the recipient.